Appearing before senators on Tuesday to testify about the marketing behind a dietary supplement known as green bean coffee extract, Dr. Oz became the target of some harsh words from Sen. Claire McCaskill, chairwoman of the Subcommittee on Consumer Protection, who accused the daytime host of giving viewers "false hope" in products.

"I don't get why you need to say this stuff when you know it's not true," McCaskill said. "When you have this amazing megaphone, why would you cheapen your show?"

Sen. McCaskill also called out Oz for endorsing FBCx, Forskolin, Garcinia cambogia and raspberry ketones as viable weight-loss supplements.

He countered by insisting that he is a "cheerleader" for the audience and his intent is to "engage viewers" with "flowery language."

"I was pleased that the hearing today dealt with some complicated issues and had all the players present whose cooperation will be necessary to move forward in protecting the consumer," Oz said in a statement following the hearing, expressing his concern about protecting his fans from weight-loss hoaxes.

"For years I felt that because I did not sell any products that I could be enthusiastic in my coverage and I believe the research surrounding the products I cover has value. I took part in today's hearing because I am accountable for my role in the proliferation of these scams and I recognize that my enthusiastic language has made the problem worse at times."

"To not have the conversation about supplements at all, however, would be a disservice to the viewer," he continued. "In addition to exercising an abundance of caution in discussing promising research and products in the future, I look forward to working with all those present today in finding a way to deal with the problems of weight-loss scams."

Here's a look at five of the weight-loss supplements under fire:

Green coffee bean extract

What Dr. Oz says: Derived from coffee beans that have yet to be roasted, Oz says, "This little bean has scientists saying they've found the magic weight-loss cure for every body type."
What we know: While there has been a study suggesting the use of green coffee bean extract supports weight loss, only a small number of people were involved. Still "using the green coffee bean extract for weight loss in my practice has proven to be very effective," says New York-based holistic practitioner and nutritionist Dr. Steven Margolin. "But we're about educating people how to take better care of themselves. Supplements assist a diet. Never just take it and eat whatever you want."

Green coffee beans

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FBCx

What Dr. Oz says: He posted on his site, "This cutting-edge fiber could have a huge weight-loss impact."
What we know: "There are some studies that say it can potentially cause weight loss," says One Medical Group physician Natasha Withers. "But those studies are very weak."

Forskolin

What Dr. Oz says: In 2012, Oz called this herbal compound "lightning in a bottle. It's a miracle flower to fight fats."
What we know: The foremost trial that supports the use of Forskolin in weight loss was sponsored by the Sabinsa Corporation – an herbal supplement manufacturer that boasts Forskolin as one of its products.

Garcinia cambogia

What Dr. Oz says: Also known as tamarind, "it may be the simple solution you've been looking for to bust your body fat for good," he said about the small pumpkin-shaped fruit.
What we know: There have been no large-scale trials suggesting it's an effective weight loss supplement. "Garcinia seems to be more effective when there's more concentrated exercise," says Dr. Margolin, adding, "exercise across the board is always going to help weight loss."

Raspberry ketones

What Dr. Oz says: He called this chemical found in red raspberries "the No. 1 miracle in a bottle to burn your fat."
What we know: Raspberry ketones have only been tested in animals; no study has officially been done on humans to support weight loss. Plus, "in terms of whether or not it's effective, the only study they've done is with raspberry ketone and vitamin C in combination, so they've never studied raspberry ketone by itself so there's no way to even say if taking it by itself is helpful," says Withers.